A copper alloy material used for a current-carrying component such as a connector, a lead frame, a relay, or a switch constituting an electric/electronic part is required to have a good electric conductivity in order to inhibit Joule heat from being generated by applying electric current and a high strength of the extent of withstanding stress imposed during the assembly or the activation of an electric/electronic part. Further, an electric/electronic part is generally formed by bending and an excellent bending workability is also requited of a material for an electric/electronic part subjected to bending. Furthermore, in order to secure contact reliability of an electric/electronic part, a material is required to be excellent in resistance to stress relaxation that is a phenomenon of lowering a contact pressure with the lapse of time, namely durability to stress relaxation.
As a method of strengthening a material used for such a current-carrying component, a method of adding a solute element such as Ni or Si abundantly, a method of repeating annealing and rolling during production, a method of increasing a finish reduction (temper treatment) ratio after aging treatment, and the like are generally known. The abundant addition of a solute element such as Ni or Si however causes the problems of increasing Ni—Si system inclusions and deteriorating bending workability. Further, the method of increasing a finish reduction (temper treatment) ratio causes the problems of lowering a cube orientation area ratio and also deteriorating bending workability.
Further, as a method of improving the bending workability of a material used for a current-carrying component, a method of lowering a finish reduction (temper treatment) ratio, a method of micronizing a crystal grain size, a method of increasing a cube orientation area ratio, and the like are generally known. If a crystal grain size is micronized however, the problem of deteriorating stress relaxation resistance is caused.
Moreover, as a method of improving the stress relaxation resistance of a material used for a current-carrying component, a method of lowering a finish reduction (temper treatment) ratio, a method of coarsening a crystal grain size, and the like are generally known.
Consequently, it can be said that, even when various conventional technologies are used, it is very difficult to simultaneously obtain the high strength, the improvement of the bending workability, and the improvement of the stress relaxation resistance of a material used for a current-carrying component constituting an electric/electronic part. As a result, a method of appropriately balancing the above characteristics in consideration of the characteristics required of a produced individual current-carrying component has heretofore had to be adopted. Among copper alloys in particular, a Corson alloy (Cu—Ni—Si system copper alloy) is recently adopted widely as a copper alloy material suitable for a current-carrying component constituting an electric/electronic part since the alloy is excellent in the above various characteristics and less expensive.
In recent years further, the downsizing and weight reduction of an electronic device advance and in particular the enhancement of strength and the reduction of thickness tend to be increasingly required of a copper alloy material used for a terminal/connector. As a result, with regard to strength, from the viewpoint of contact pressure strength in particular, a high 0.2% proof stress (YP) in the direction perpendicular to a rolling direction (T. D. direction) tends to be required.
A specific characteristic of a Corson alloy however is that the difference in strength is large between in the direction parallel with a rolling direction (L. D. direction) and in the direction perpendicular to a rolling direction (T. D. direction), namely the strength in the direction perpendicular to a rolling direction is relatively lower than the strength in the direction parallel with a rolling direction. Another characteristic is that the difference between a tensile strength (TS) and a 0.2% proof stress (YP) is large. Consequently, when a Corson alloy is used for a terminal/connector, the problems of lowering a proof stress in the direction perpendicular to a rolling direction and lacking contact pressure strength are caused.
In recent years, various methods are proposed for improving the bending workability of a Corson alloy. In JP-A No. 2006-152392 for example, as a method effective in improving the bending workability of a Corson alloy, a technology of controlling the texture of crystal grains is proposed. In JP-A No. 2006-152392, disclosed is a copper alloy plate that: comprises a Corson alloy containing Ni by 2.0 to 6.0 mass % and Si in the range of 4 to 5 in terms of an Ni/Si mass ratio; has a texture wherein the average crystal grain size is controlled to not larger than 10 μm and the proportion of the cube orientation {001}<100> is not less than 50% in the measurement result by an SEM-EBSP method; and does not have a lamellar boundary observable by texture observation with an optical microscope of 300 magnifications.
In JP-A No. 2009-7666 further, described is a proposal on a copper alloy for an electric/electronic device having R{200} of 0.3 or more when a diffraction intensity from a {111} plane is defined as I{111}, a diffraction intensity from a {200} plane is defined as I{200}, a diffraction intensity from a {220} plane is defined as I{220}, a diffraction intensity from a {311} plane is defined as I{311}, and the ratio of the diffraction intensity from the {200} plane in the diffraction intensities is defined as R{200}=I{200}/(I{111}+I{200}+I{311}) on the surface of a copper alloy material containing Ni by 0.5 to 4.0 mass %, Co by 0.5 to 2.0 mass %, and Si by 0.3 to 1.5 mass %.
In JP-A No. 2008-13836 further, described is a proposal on a copper alloy plate material retaining a high strength and an excellent bending workability of a Corson alloy and simultaneously having improved anisotropies of those characteristics by satisfying the expressions 3.0≦I{220}/I0{220}≦6.0 and 1.5≦I{200}/I0{200}≦2.5 in a copper alloy plate material containing Ni by 0.7% to 2.5% and Si by 0.2% to 0.7% in terms of mass %.
In JP-A No. 2008-223136 further, described is a proposal on a copper alloy plate material retaining a high strength and a high electric conductivity and simultaneously exhibiting excellent bending workability and stress relaxation resistance by satisfying the expression I{420}/I0{420}>1.0 in a copper alloy plate material containing Ni by 0.7% to 4.2% and Si by 0.2% to 1.0% in terms of mass %.
In JP-A No. 2010-275622 further, described is a proposal on a copper alloy plate material retaining a high strength, simultaneously having an excellent bending workability of low anisotropy, and also having an excellent stress relaxation resistance by having a crystalline orientation satisfying the expression I{200}/I0{200}≧1.0 when the X-ray diffraction intensity of a {200} crystal plane on a plane of a copper alloy plate containing Ni by 0.7 to 4.0 mass % and Si by 0.2 to 1.5 mass % is defined as I{200} and the X-ray diffraction intensity of a {200} crystal plane of pure copper standard powder is defined as I0{200}.